The pronunciation of the BATH vowel is a salient feature of English varieties of the southwest of England, yet neither the status of the TRAP–BATH split in traditional dialects nor ongoing change today is well understood. After reviewing the existing literature, we investigate the quality and length of low unrounded vowels in Bristol English on the basis of sociolinguistic interviews with twenty-five speakers. The picture suggested by these data is complex: there is evidence for a traditional length-only TRAP–BATH split, for a length and backness split diffusing from the east and for a merger diffusing from the north. Some of these changes involve lexical diffusion, especially with loanwords and other distinctive lexical groups. Overall, the rich and contradictory data speak to the contested sociolinguistic status of these variables and to the need to examine individual patterns of variation closely to gain a full understanding of them.